Field of the Invention
The invention lies in the telecommunications field. More specifically, the invention relates to a method and a radio communications system for controlling signaling, in particular in a mobile radio system.
In radio communications systems, useful data, for example voice, image information or other data are transmitted between a transmitting radio station and a receiving radio station via a radio interface using electromagnetic waves. The electromagnetic waves are thereby broadcast with carrier frequencies which lie in the frequency band that is provided for the respective system. In the conventional GSM mobile radio system (Global System for Mobile Communications), as is known, inter alia, from J. Biala, xe2x80x9cMobilfunk und intelligente Netzexe2x80x9d [Mobile Radio and Intelligent Networks], Vieweg Verlag, 1995, in particular pages 57-92, the carrier frequencies are in the range of 900 MHz, 1800 MHz and 1900 MHz. Future radio communications systems, for example the UMTS (Universal Mobile Telecommunications System) or other third generation systems, frequencies in the approximately 2000 MHz frequency band are provided. In order to distinguish between different signaling sources at the location of the respective receiver it is possible to use frequency multiplex (FDMA=frequency division multiple access), time-division multiplex (TDMA=time division multiple access), and/or code multiplex methods (CDMA=code division multiple access), as well as a combination of these known methods.
The above-mentioned Biala description (see page 78) discloses a GSM mobile radio system wherein a mobile station uses, for a connection set-up, a common access signaling channel RACH (Random Access (Control) Channel) for requesting a transmitting channel at a base station. In order to prevent blocking when there is simultaneous access of a plurality of mobile stations to the signaling channel, the access takes place according to a method with random access timing, a so-called slotted Aloha protocol. As a confirmation in response to the connection request, the base station directly assigns a transmission channel on a confirmation signaling channel (AGCH) (Access Grant Channel), or provides a reference to a specific signaling channel SDCCH (Stand-Alone Dedicated Channel) for the further standard connection set-up procedure.
In addition to the use for a connection set-up, the access signaling channel RACH is used for further services such as connection management (CM) and mobility management (MM).
The connection management service carries out, inter alia, functions such as call control, supplementary service signaling or even short message signaling. On the other hand, the mobility management service covers all the tasks which arise from the mobility of the mobile stations. It includes, inter alia, the localization and updating of the positions of the mobile stations.
In future third generation radio communications systems, a common use of, for example, the access signaling channel for a plurality of different services is planned in order to utilize more effectively the capacity of the radio resources.
It is accordingly an object of the invention to provide a method and a base station for a communications system, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which prevents blocking of the signaling channel which is used jointly for a plurality of services.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method of controlling signaling in a radio communications system, which comprises:
transmitting signals of a service in a common signaling channel in an up-link direction from a plurality of radio stations to a base station of a radio communications system;
transmitting signals in a further signaling channel in a down-link direction from the base station to the radio stations;
assigning service classes to the services;
selecting, with the base station, possible service classes for further processing, depending on a function of a traffic volume currently determined in the common signaling channel;
signaling, with the base station, the selected service classes to the radio stations in the further signaling channel; and
taking into account, with the radio stations, the selected service classes for access to the common signaling channel.
In other words, the signals of a service are transmitted in a common signaling channel in the up-link direction from the radio stations to the base station of the radio communications system. In the other direction, the signals are transmitted in a further signaling channel in the down-link direction from the base station to the radio stations. Service classes are assigned to the services so as to characterize them. The base station selects possible service classes for further processing, as a function of a traffic volume which is instantaneously determined in the common signaling channel, and signals them to the radio stations in the further signaling channel. In response, the radio stations take into account the selected service classes for access to the common signaling channel.
The invention has the advantage that by virtue of the assignment of the services to service classes in the base station it is possible to select which services are, for example, available to the radio stations at any time and which services are, for example, not further processed when there is a high traffic volume in the common signaling channel. As a result, overloading or blocking of the common signaling channel owing to a high signaling load is advantageously prevented.
This has a particularly advantageous effect if, according to further developments, signals of services relating to connection management, mobility management and/or transmission of packet data are transmitted by the radio stations. In this context, it is possible, for example, to assign the services of the connection management and mobility management, which are highly significant for a safeguarded connection and a constant high transmission quality in a radio communications system which is embodied as a mobile radio system, a higher priority than the transmission of packet data, so that when the traffic volume is high the connection management and mobility management service classes are selected and signaled to the radio stations. In the same way, it is possible to restrict the connection management service if, for example, all the transmission channels are assigned and it is not possible to set up any further communications connections via the base station. The respectively selected service classes can be taken into account in the radio stations in such a way that the radio stations only ever transmit signals of the selected services to the base station.
In accordance with an added feature of the invention, a first service class is assigned to a service relating to connection management, a second service class is assigned to a service relating to mobility management, and a third service class is assigned to a service relating to a packet data transmission.
In accordance with an additional feature of the invention, the selected service classes are each characterized by an information element in a signaling message in the further signaling channel. The signaling message according to the invention makes it advantageously possible for the radio stations to transmit signals of services in accordance with the service classes which have been selected by the set information elements.
In accordance with another feature of the invention, an instantaneous traffic volume in the common signaling channel is determined in the base station or in a device for assigning radio resources of the radio communications system.
In accordance with a further development of the invention, the instantaneous traffic volume is determined periodically at predefined time intervals and/or when the instantaneous traffic volume changes. This makes it advantageously possible for the signaling of the selected services to be adapted to the respective instantaneous change in the traffic volume, the radio stations being at all times informed of which services they can access. Furthermore, by means of an optimized time interval it is possible advantageously to minimize the signaling load without negative effects in terms of capacity utilization of the common signaling channel occurring.
In accordance with two alternative developments of the invention on the first hand the instantaneous traffic volume of the respective service classes is compared with a threshold value for a maximum traffic volume. When the threshold value is exceeded the respective service class is not selected for further processing. On the other hand, the traffic volume in the signaling channel is compared with at least one threshold value for a maximum traffic volume. If the threshold value is respectively exceeded a specific service class is not selected for further processing.
The first alternative development makes it advantageously possible for an appropriate transmission capacity to be assured for the corresponding service classes in the common signaling channel at any time by virtue of the comparison of each service class with a threshold value. In this context, it is also conceivable that, for example, only the traffic volume for the service of the transmission of data packets is compared with the threshold value. If this threshold value is exceeded, it is signaled to the radio stations that only the further services which are still selected can be accessed. An exemplary restriction of the transmission of data packets is not critical owing to the transmission which is not dependent on real time, because the transmission of the data packet can be reset by the radio station until sufficient transmission capacity is available again in the common signaling channel.
The second alternative development has the advantage that only the entire traffic volume in the signaling channel is determined and in each case the service classes which are necessary for optimum operation of the radio communications system are selected in each case as a function of said traffic volume. Thus, for example when there is a high traffic volume, firstly the transmission of packet data, and subsequently the mobility management, are restricted in order to ensure at least a safeguarded connection set-up and release. On the other hand, it is possible, for example, to restrict the connection management if all of the transmission channels which are available to the base station are being used. The respective threshold values can be set here by, for example, the network operator, because he has considerable interest in a continuously high transmission quality and connection reliability.
In accordance with again an added feature of the invention, the common signaling channel used is an access signaling channel which is accessed by the radio stations according to a randomly controlled slotted ALOHA method. This access signaling channel can be based, for example, on the access signaling channel which is known from the GSM mobile radio system and whose function has been described above in the introduction to the description.
In accordance with again an additional feature of the invention, the further signaling channel used is a common signaling channel in which general system information of the radio communications system is transmitted, or a connection-specific confirmation signaling channel is used. The common signaling channel is monitored by all the radio stations which are located in the radio coverage area of the base station, and the system information of said channel is read out and evaluated. The connection-specific confirmation signaling channel has the advantage that the selected service classes are signaled in each case only to the radio stations which access the common signaling channel, as a result of which the general signaling load in the radio communications system is advantageously reduced.
The further signaling channel can be based on the Broadcast Control Channel (BCCH) known from the GSM mobile radio system, or on the Access Grant Channel (AGCH), such as were described in the introduction to the description and which are supplemented in each case with additional signaling information. This refinement of the signaling channels on the basis of known signaling channels has the advantage that compatibility between, for example, second and third generation mobile radio systems is made possible, in which case the additional information is, for example, not recognized or taken into account by the older system.
With the above and other objects in view there is also provided, in accordance with the invention, a radio communications system for controlling signaling, which comprises:
a base station;
a plurality of radio stations each having a control device and having a transceiver device for transmitting respective signals of a service in a common signaling channel in an up-link direction to the base station;
the base station having a transceiver device for transmitting signals in a further signaling channel in a down-link direction to the radio stations;
a control device in the base station for selecting possible service classes assigned to the services, for further processing as a function of an instantaneous traffic volume in the common signaling channel, and for making available the selection for the transceiver device for signaling the selected service channels in the further signaling channel; and
the respective control device in the radio stations taking into account the selected service classes for access to the common signaling channel.
In accordance with yet an added feature of the invention, a device is provided in the base station for determining the instantaneous traffic volume in the common signaling channel or a respective instantaneous traffic volume of the service classes.
In accordance with yet an additional feature of the invention, a radio resource assignment device connected to the base station for assigning radio resources, the radio resource assignment device having a device for determining one of the instantaneous traffic volume in the common signaling channel and the respective instantaneous traffic volume of the service classes.
In accordance with yet another feature of the invention, an evaluation device is provided in the base station for comparing the instantaneous traffic volume with a threshold value.
In accordance with a concomitant feature of the invention, a timer in the base station initiates a determination of the instantaneous traffic volume in the common signaling channel at specific time intervals.
It is thus clear that the method according to the invention is particularly advantageously used in a radio communications system which uses a CDMA subscriber separation method or a combination of a CDMA method with further subscriber separation methods. A parallel use of a frequency band for a plurality of communications connections is common to these methods, the individual connections being differentiated by individual spread codes. As a result, in comparison with the known GSM mobile radio system, a relatively large number of radio stations can access the common signaling channel in parallel, and correspondingly cause this channel to be overloaded.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method and radio communications system for controlling signaling, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.